Method of manufacturing a magnetic member having a coating of crystalline ferromagnetic material having uniaxial magnetic anisotropy



United States Patent METHOD OF MANUFACTURING A MAGNETIC MEMBER HAVING A COATING 0F CRYSTAL- LINE FERROMAGNETIC MATERIAL HAVING UNIAXIAL MAGNETIC ANISOTROPY Frank G. Brockman, Dobbs Ferry, N.Y., assignor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware N0 Drawing. Filed Sept. 24, 1963, Ser. No. 311,204

8 Claims. (Cl. 117-7) My invention relates to a method of manufacturing a thin film with uniaxial anisotropy, particularly thin films for magnetic memory devices.

Films of magnetic material have been used as storage devices for memory systems in digital computers. In order that the films can function in these memories at high speeds, the films are usually quite thin. In addition, it is desirable that the film have two stable states of magnetization, so that the information can be stored in a yes or no fashion. Thin films have been made by (1) evaporation (2) sputtering and (3) electrodeposition, and in any of these three methods, the thickness of the deposited layer of magnetic material is subject to control (chiefly by the time of deposition under otherwise controlled conditions). The introduction of the two stable states is usually accomplished by carrying out the deposition in the presence of a magnetic field. These films with the two stable states are said to possess uniaxial anisotropy, and in this case the uni-axial anisotropy is said to have been induced in the film by the magnetic field applied during deposition.

A principal object of my invention is the provision of a new and novel method of manufacturing a thin film with uniaxial anisotropy without the aid of a magnetic field.

A further object of my invention is to provide a method of manufacturing a stressed thin film which has uniaxial anisotropy.

These and further objects of the invention will appear as the specification progresses.

According to this invention, the deposited film is rendered anisotropic and given uniaxial form of anisotropy by first subjecting the substrate, on which the thin film is later deposited to a unidirectional stress, thus placing the substrate in strain. The thin film is now deposited upon the substrate. When the stress is removed from the substrate, the stress will be transferred to the thin film, which thereby will be placed under strain and will, as a result, exhibit uniaxial anisotropy.

In one particular embodiment of the invention, the substrate is given a cylindrical curvature, either concave or convex, and the thin film deposited on the surface thereof, after which the force on the substrate is removed. The thin film is thereby placed under either tensile or compressive stress and will exhibit uniaxial anisotropy.

In another embodiment of the invention, the substrate may be rigidly secured along one edge While the opposite edge is subjected to a force which will either compress or elongate the substrate. After the thin film is deposited on the surface of the substrate, the compressive or tensile force on the substrate is removed placing the thin fihn under tensile or compressive stress resulting in uniaxial anisotropy in the film.

It is essential, however, that the substrate should not be stressed beyond its elastic limit.

3,303,040 Patented Feb. 7, 1967 The invention will be described in connection with the following illustrative example.

A body of glass is rigidly clamped at one end and the opposite end clamped and stretched to place the glass under tensile stress. While the glass is under tensile stress, a layer of an alloy of 82% nickel and 18% iron, having a thickness of about lOOO Angstrom units, is deposited by evaporation onto the surface of the glass. After the layer is deposited, the tensile force on the glass is released placing the layer under compressive stress. The resulting layer now possesses uniaxial anisotropy such that the metal film has a preferred axis of magnetization.

Instead of a glass body, a ceramic body could have been employed. Alternatively, a metal body could also have been employed which could have been bent and allowed to return to its original shape.

Furthermore, the invention is not restricted to the for mation of magnetic thin films. Any crystalline material can be deposited and uniaxial anisotropy produced therein by depositing the crystalline material, e.g. by evaporation, sputtering, or electroplating on a pre-stressed substrate which is allowed to return to its unstressed state transfering the stress to the superposed layer thereon.

Therefore, while the invention has been described with reference to specific examples and applications thereof, other modifications will be readily apparent to those skilled in this art without departing from the spirit and scope Oif the invention as defined in the appended claims.

What I claim is: v

1. A method of manufacturing a magnetic member having a non-magnetic substrate coated with a layer of crystalline ferromagnetic material having uniaxial magnetic anisotropy comprising the steps of unidirectionally stressing the substrate below the elastic limit thereof thereby placing the substrate in strain, coating the stressed substrate with a thin film of the ferromagnetic material having a thickness substantially less than that of the substrate and subsequently removing the stress from the substrate and transferring the strain therein to the film producing uniaxial anisotropy therein.

2. A method of manufacturing a magnetic member as claimed in claim 1, in which the substrate is subjected to a tensile force to unidirectionally stress the substrate.

3. A method of manufacturing a mganetic member as claimed in claim 1, in which the substrate is subjected to a compressive force to unidirectionally stress the substrate.

4. A method of manufacturing a magnetic member as claimed in claim 1, in which the substrate is coated by evaporating a crystalline magnetic material.

5. A method as claimed in claim 1, in which the coating is applied by sputtering a crystalline magnetic material.

6. A method as claimed in claim 1, in which the coating is applied by electroplating a crystalline magnetic material.

7. A method as claimed in claim 1, in which the magnetic material is a nickel-iron alloy and the substrate is glass.

8. A method of producing uniaxial anisotropy in a thin fihn of crystalline material comprising the steps of unidirectionally stressing a substrate below the elastic limit thereof thereby placing the substrate in strain, coating the stressed substrate with a thin layer of ferromagnetic crystalline material to form a thin film, and subsequently removing the stress from the substrate and transferring the strain to the layer producing uniaxial anisotropy therein.

(References on following page) References Cited by the Examiner UNITED STATES PATENTS Wissler 11743 X Newcomb 117-101 X Blume 18-55 Mitchell 117- 107 Lytle 1178 X Eckert 204-192 Averbach 117--107.1

Bennett 117-107.2

Henkes 346--74 WILLIAM D. MARTIN, Primary Examiner.

W. D. HERRICK, Assistant Examiner. 

1. A METHOD OF MANUFACTURING A MAGNETIC MEMBER HAVING ANON-MAGNETIC SUBSTRATE COATED WITH A LAYER OF CRYSTALLINE FERROMAGNETIC MATERIAL HAVING UNIAXIAL MAGNETIC ANISOTROPY COMPRISING THE STEPS OF UNIDIRECTIONALLY STRESSING THE SUBSTRATE BELOW THE ELASTIC LIMIT THEREOF THEREBY PLACING THE SUBSTRATE IN STRAIN, COATING THE STRESSED SUBSTRATE WITH A THIN FILM OF THE FERROMAGNETIC MATERIAL HAVING A THICKNESS SUBSTANTIALLY LESS THAN THAT OF THE SUBSTRATE AND SUBSEQUENTLY REMOVING THE STRESS FROM THE SUBSTRATE AND TRANSFERRING THE STRAIN THEREIN TO THE FILM PRODUCING UNIAXIAL ANISOTROPY THEREIN. 